1. Technical Field
The present invention is related to a linear type vibration motor having a magnet casing.
2. Description of the Related Art
A vibration motor is a part that converts electrical energy into mechanical vibrations by using the principle of generating electromagnetic forces, and is commonly installed in a mobile phone to generate a soundless vibrating alert. With the rapid expansion of mobile phone markets and increased functionalities added to the mobile phone, mobile phone parts are increasingly required to be smaller and better. As a result, there has been an increased demand for the development of a new structure of vibration motor that can overcome the shortcoming of conventional vibration motors and effectively improve the quality.
As mobile phones having a bigger LCD screen have become popular for the past few years, there have been an increasing number of mobile phones adopting a touch-screen method, by which the body or screen of a mobile phone is vibrated when a user touches an input unit of the mobile phone in order to provide the user an appealing sensory feel when touching the touch screen. Commonly used to generate the vibration is a vibration motor.
The touch-screen method particularly requires that the vibration motor has a greater durability due the a greater frequency of generating vibrations in response to the touch compared to the vibration bell for incoming calls and that the vibration motor has a faster response to the touch made on the touch screen, in order to provide the user a greater satisfaction from sensing the vibration when touching the touch screen.
The conventional vibration motors commonly used in mobile phones generate a rotational force to cause mechanical vibrations by rotating an eccentric rotor. The rotational force is generated by supplying an electric current to the coil of a rotor by using the rectifying action of a brush and a commutator.
The vibration motor using such brush and commutator has a shorter operating lifetime due to mechanical friction and electrical sparks, which cause wear and black powder, while the brush moves between the segments of the commutator when the motor rotates. Moreover, when voltage is supplied to the vibration motor, it takes time to reach the target amount of vibration, i.e., the magnitude by which it is sufficient for the user to sense the vibration, by the rotational inertia of the vibration motor, causing a slower response to the touch made on the touch screen.
Developed to overcome the drawbacks of shorter operating lifetime and slower responsiveness is a linear type vibration motor. The linear type vibration motor does not use the principle of rotation of a motor but uses an electromagnetic force having a predetermined resonant frequency to generate vibrations by use of an elastic body installed in the vibration motor and the mass of a weight elastically supported by the elastic body.
Here, the electromagnetic force is generated by a direct or alternating current supplied to a coil. More specifically, a direct or alternating current having a frequency considering the modulus of elasticity of the elastic body and the mass of the weight is applied to a coil to allow the linear type vibration motor to generate vibrations that correspond to the resonant frequency.
Used to form the magnetic body, which is vibrated by the electromagnetic force generated by the coil, is a magnet assembly, in which a pair of magnets are disposed in such a way that same magnetic poles face each other in order to increase the density of magnetic flux penetrating through the coil in a perpendicular direction to the coil. This will be described with reference to FIG. 1.
Illustrated in FIG. 1 is a conventional magnet assembly.
Referring to FIG. 1, a magnet assembly 140 is constituted by a core 142, a first magnet 143 and a second magnet 144. The first magnet 143 and the second magnet 144 are coupled to either side of the core 142 by use of an adhesive. While the core 142 is interposed between the first magnet 143 and the second magnet 144, the polarity of the first magnet 143 faces the same polarity of the second magnet 144. In other words, the first magnet 143 and the second magnet 144 are disposed in such a way that same magnetic poles face each other.
Here, as illustrated in FIG. 1, the first magnet 143 and the second magnet 144 are disposed in such a way that the N-poles are placed on either end of the magnet assembly 140, respectively. Although it is not illustrated in FIG. 1, they can be disposed in such a way that the S-poles are placed on either end of the magnet assembly 140.
The magnet assembly 140 vibrates frequently, and if a mobile phone having a linear type vibration motor embedded therein is dropped from a high position due to, for example, the user's carelessness, a strong shock is applied to the magnet assembly 140. In this case, since the first magnet 143 and the second magnet 144 are coupled to the core 142 by an adhesive, as described above, they may be separated from one another by the vibration or shock. This may cause malfunction of the linear type vibration motor.